METABOLISM, NUTRITION AND DIETETICS 557 



sufficient to encourage the hope that it may possess some thera- 

 peutic value, although far from what has been claimed for it 

 by its more enthusiastic advocates. The only constituent of 

 extracts of the testicle made with salt solution which causes 

 any pronounced effect on the blood-pressure when injected into 

 the circulation is a nucleo-protein, the most plentiful of the pro- 

 tein substances. The pressure falls, mainly owing to inhibition 

 of the heart, but partly through vaso-dilatation in the splanchnic 

 area (Dixon). 



The testicles also influence the growth of the bones. In 

 eunuchs and in young men with atrophy of the testicles a ten- 

 dency has been observed for the long bones to go on growing 

 far beyond the usual period. This has been shown by the 

 Rongten rays to be due to delay in the ossification of the epi- 

 physes. The same has been observed in animals, and is supposed 

 to be caused by the loss of some substance normally formed in 

 the testicle which influences the metabolism of the bones and 

 the deposition of the bone salts. 



A temporary diminution in the haemoglobin and in the number 

 of the erythrocytes has been observed in castrated bitches, an 

 observation which, so far as it goes, is in favour of the view that 

 an insufficient internal secretion of the ovaries is the cause of 

 the form of anaemia known as chlorosis. 



Evidence has recently been brought forward that the corpus 

 luteum is a gland with an internal secretion, whose function 

 is connected with menstruation and with the implantation of 

 the ovum and the subsequent growth of both ovum and uterus 

 in pregnancy (Born, Fraenkel) (Chap. XIV.). 



Thymus. It is well known that in castrated animals the 

 thymus is larger and persists longer than in entire animals. In 

 bulls and unspayed heifers the normal atrophy of the thymus, 

 which begins after the period of puberty, is greatly accelerated 

 when the bulls have been used for breeding, and when the heifers 

 have been pregnant for several months. There is a reciprocal 

 influence of the thymus on the testicles, and removal of the 

 thymus before the time at which it naturally atrophies is fol- 

 lowed by a more rapid growth of the testes (in guinea-pigs) 

 (Paton). In young mammals the loss of the thymus causes 

 transient disturbances of nutrition, a temporary decrease in 

 the number of all varieties of leucocytes, and a diminished 

 resistance to the pus-forming micrococci, probably connected 

 with the relatively feeble leucocytosis (or increase in the number 

 of leucocytes) by which the animals react to the infection. In 

 the frog the thymus persists throughout life. Yet the removal 

 of it is not fatal if precautions against infection be taken. In 

 mammals (including man) the thymus does not completely 



